Characteristics of tunneling and impact ionization in ZnS:Mn-based thin-film electroluminescent structures

A method for measuring the characteristics of tunneling and impact ionization in thin-film electroluminescent emitters is suggested. This method makes it possible to find time dependences of the space-charge layer thickness near the anode and the length of the impact ionization region, to determine more exactly the time dependence of the field in the potential barrier at the cathode interface, the maximum depth of the surface states from which electron tunneling occurs, the minimum thickness of the barrier, and the electron tunneling probability, as well as the impact ionization rate for the deep centers related to structural defects of the phosphor layer.     

The effect of photoexcitation of the electrical properties of ZnS:Mn thin-film emitters

Significant distinctions have been observed in the current kinetics and current-voltage characteristics of ZnS: Mn electroluminescent thin-film emitters measured with pulsed photoexcitation in different (blue, red, and infrared) spectral intervals. The results show evidence that a recharge of deep centers related to the zinc and sulfur vacancies takes place in the course of the emitter operation, leading to the formation of space charges in the near-anode and near-cathode regions of the phosphor layer.     

High-power laser diodes (λ = 808–850 nm) based on asymmetric separate-confinement heterostructures

Symmetric and asymmetric separate-confinement AlGaAs/GaAs heterostructures have been grown by MOCVD in accordance with the concept of design of high-power semiconductor lasers. High-power laser diodes with a 100-μm aperture, emitting in the 808–850-nm range, were fabricated from these structures. The internal optical loss in asymmetric separate-confinement heterostructures with broadened waveguide is reduced to 0.5 cm⁻¹. In the lasers with 1.7-μm-thick waveguide, the output optical power of 7.5 W in CW mode was achieved owing to reduction of the optical emission density at the cavity mirror to 4 mW/cm². Original Russian Text ? A.Yu. Andreev, A.Yu. Leshko, A.V. Lyutetskiĭ, A.A. Marmalyuk, T.A. Nalyot, A.A. Padalitsa, N.A. Ptkhtin, D.R. Sabitov, V.A. Simakov, S.O. Slipchenko, M.A. Khomylev, I.S. Tarasov, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 628–632.     

Instantaneous emission brightness kinetics of zinc sulfide based electroluminescent thin-film emitters

Excited with triangular voltage pulses, electroluminescent thin-film emitters based on manganese-doped zinc sulfide exhibit a two-stage buildup and decay of the instantaneous emission brightness. The fast decay stage corresponds to the Mn²⁺ ion relaxation in zinc sulfide at a time constant of 1.4 ms. Preceding the fast stage, the slow decay stage has a time constant ten times greater and accounts for a markedly increased afterglow (phosphorescence) duration. The luminance level corresponding to the transition from the first to second stage is virtually independent of the applied voltage and the charge passed through the luminophor.     

Feedback control of one-link flexible manipulator with gear train

This article reports experimental results in control of a one-link flexible manipulator. A d.c. drive with gear train rotates the link with a tip-mass in the horizontal plane. A “stiff” hardware servo-system tracks the commanded drive velocity. We describe the experimental setup and develop a dynamic model for the one-mode flexible vibration control. We design and experimentally test controllers for active damping of the vibrations and stabilization of the link-tip position. Results for continuous control implemented with an analog computer and a sampled-data, digital-computer control are reported. A high control performance is achieved despite the gear-train friction influence. In addition, sampled-data digital controllers for tracking control of the link reference motion are designed and tested.     

Switch-off relaxation of the parameters of ZnS:Mn thin-film electroluminescent emitters

We have experimentally studied the decay of a current transferred via a phosphor layer in ZnS:Mn thin-film electroluminescent emitters. It is established that this decay is controlled by a bimolecular process of electron trapping on the surface states at the anode phosphor-insulator interface. The rate of the surface trapping, the trapping cross section, and the electron lifetime at the onset of current decay are determined. Dependences of these parameters on the polarity, amplitude, and frequency of the triangular voltage pulses have been studied.     

Thin-film electroluminescent emitters on rough substrates

For thin-film ac electroluminescent emitters prepared on rough glass substrates in combination with the use of a layer of liquid-crystal insulating composite, a twofold increase has been observed in the emission brightness as compared with the usual emitters prepared on smooth substrates. Pis’ma Zh. Tekh. Fiz. 23, 7–12 (August 12, 1997)     

A new method for estimating the electroluminescence parameters of ZnS:Mn thin-film emitters

We describe a new method for estimating the electroluminescence parameters of ZnS:Mn thin-film emitters based on an analysis of the experimental kinetic curves of the instantaneous internal quantum yield in the first half-period of the excitation voltage at a low-frequency for which the current buildup rate does not exceed the luminance growth rate. Using the proposed method, it is possible to evaluate (i) the probability of radiative relaxation in Mn²⁺ centers upon their electron-impact excitation, (ii) the time variation of the electron multiplication coefficient, (iii) the number of ionization events per electron escaped from the ionization region, and (iv) the length of the impact excitation of the emitting centers.     

Characteristics of surface states at the insulator-semiconductor interface of ZnS:Mn thin-film electroluminescent emitters

The energy distribution of the density of occupied surface states (N _ss) at the cathode insulatorphosphor interface in ZnS:Mn electroluminescent thin-film (ELTF) emitters has been modeled on the basis of experimental data. Changes in this distribution depending on the parameters of exciting voltage pulses have been studied. It is established that the energy distribution of N _ss shifts toward deeper levels upon a decrease in the frequency of the exciting signal and the resulting increase in the pause between the adjacent switch-on states. This behavior corresponds to a cascade relaxation mechanism of electrons trapped on the surface states. Maximum values of the N _ss (∼2.5 × 10¹³ cm⁻²) and the specific density of surface states per unit energy (2 × 10¹⁴–10¹⁵ cm⁻² eV⁻¹) are determined for the cathode insulator-phosphor interface from which electrons are tunneling. Positions of the equilibrium (∼1.25 eV below the conduction-band bottom) and the quasi-equilibrium (0.6–1.25 eV) Fermi levels during the ELTF emitter operation are estimated.